Method for operating an internal combustion engine of a vehicle, especially a motor vehicle, and device for implementing said method

ABSTRACT

The invention relates to a method for operating an internal combustion engine of a vehicle, particularly a motor vehicle, wherein the nitrogen content in an intake air flow ( 1 ) suctioned from the ambient air is reduced before delivering the air flow to at least one combustion chamber of the internal combustion engine ( 7 ) in order to produce a nitrogen-reduced combustion air flow whose oxygen content is higher than that of the suctioned air flow. According to the invention, the suctioned air flow ( 1 ) is run past or along at least one porous solids body ( 5 ) in at least one partial area of the intake air flow path ( 3 ), the size of the pores of said solids body being designed in such a way that the quantity of nitrogen molecules drawn off from the intake air flow ( 1 ) through the porous solids wall ( 5 ) is larger than the quantity of oxygen molecules drawn off from the oxygen or nitrogen molecules of the intake air flowing past the porous solids body ( 5 ) in order to form the nitrogen-reducing and oxygen-enriched combustion air flow that is supplied to the at least one combustion chamber ( 7 ) as main partial gas flow ( 8 ) and at least one nitrogen-enriched and oxygen-reduced secondary partial gas flow ( 9 ) which is not delivered to the at least one combustion chamber ( 7 ).

This application is a §371 application of PCT/EP2004/005597, whichclaims priority from DE 10325413.7, filed Jun. 5, 2003.

The invention relates to a method for operating an internal combustionengine of a vehicle, especially a motor vehicle, as specified in thepreamble of claim 1, and to a device for implementing said method asspecified in the preamble of claim 11.

Pretreatment of ambient air introduced into a combustion chamber of aninternal combustion engine as combustion air, which usually is made upof 21% oxygen, 78% nitrogen and 1% residual gas, for reduction of thepollutant components of the internal combustion engine is generallyknown. For example, DE 197 10 840 A1 has disclosed provision of anenrichment channel communicating with an intake channel, a membranepermeable by oxygen molecules being mounted in the enrichment channel.As a result of the partial vacuum predominating in the intake channel,ambient air is drawn through the membrane and is subsequently enrichedwith oxygen on the outlet side. In the area of opening of the enrichmentchannel into the intake channel the ambient air normally drawn in isadmixed with the oxygen-enriched air coming from the enrichment channelbefore this air is introduced into the combustion chamber as combustionair.

DE 195 43 884 A1 discloses a process in which an oxygen-enriched volumeflow is obtained as permeate in a complex process in a noncryogenicseparation unit from an air volume flow and is introduced into theinternal combustion engine. The oxygen-enriched volume flow from thenoncryogenic separation unit is compressed and temporarily stored in abuffer tank from which it is taken as needed.

DE 197 10 842 A1 discloses a process for reduction of pollutants andcombustion exhaust gases of internal combustion engines, a process inwhich combustion air of increased oxygen content is introduced into theinternal combustion engine, the combustion air being obtained fromambient air by a membrane mounted in a chamber and being permeable onlyby oxygen molecules. In order to reduce the light-off time of thecatalytic converter so as to permit reduction of the toxic emissiondownstream from the catalytic converter, the application proposes thatthe gas with an increased oxygen component be admixed with the intakeair as a function of the operating point of the internal combustionengine.

DE 199 12 137 A1 discloses an internal combustion engine with oxygenenrichment such that the internal combustion engine has a gasaccumulator for storage of oxygen-enriched gas which has been produced,means being provided for delivery of oxygen-enriched gas to the internalcombustion engine during a cold-start phase until a specified warm-airoperating state of the internal combustion engine has been reached. Whenthe internal combustion engine is in warmed-up operation, temporarilyoxygen-enriched gas is produced from air by means of an oxygenseparation unit and stored at least for a brief period in the gasaccumulator.

A process and structure similar to that of DE 197 10 840 A1 have alsobeen disclosed in DE 44 04 681 C1, in which at least one channelconducting the oxygen-nitrogen air mixture is associated with an exhaustgas channel connected to the combustion chamber, is provided with apartition permeable by oxygen or stores oxygen, and oxygen is deliveredexclusively by way of it to the combustion exhaust gas of a combustionchamber.

DE 42 01 423 A1 discloses a process in which a complex gas permeationsystem is mounted upstream from a diesel internal combustion engine sothat the combustion air conducted to the diesel internal combustionengine is first filtered in its entirety through a membrane forgeneration of an oxygen-enriched combustion air flow.

Another generic process for operation of an internal combustion engineof a motor vehicle is disclosed in WO 01/18369 A1. Specifically, anitrogen absorber is provided in this instance as gas separation unit,but it is very costly and complex in structure. In this instance theoxygen-enriched gas is then admixed, again by way of a separate channel,with the non-oxygen-enriched combustion air drawn in from the ambientatmosphere.

All these conducts of the process and structures have in common thefeature that oxygen-enriched air is admixed with the air stream drawn infrom the ambient air by way of a separate delivery channel or thecombustion air drawn in is filtered in its entirety through a membranefor the purpose of enrichment with oxygen prior to delivery to thecombustion chamber. Such structures present the problem that, in thefirst instance, a high equipment-engineering and civil engineeringeffort is required and, in the second instance, the danger exists thatmembranes may at some point in time become clogged so that delivery tothe combustion chamber of the air flow required is no longer guaranteed.Conversion and application for use in series is accordingly difficult inthis case.

The object of the invention is to make available a process for operationof an internal combustion engine of a vehicle, a motor vehicle inparticular, and a device for implementation of such a process, a processand device by means of which oxygen enrichment of combustion airintroduced into a combustion chamber of the internal combustion enginemay be effected by simple means dependable in operation.

According to one embodiment of the invention the intake air flow isconducted over at least one partial area of the intake flow air pathpast and/or along at least one porous solid-state wall, the size of thepores of which is configured so that, of the oxygen and nitrogenmolecules flowing past along the porous solid-state wall, a greaternumber of nitrogen molecules than of oxygen molecules pass through theporous solid-state wall. This results in formation of at least onenitrogen-reduced and oxygen-enriched combustion air flow which may beintroduced into the at least one combustion chamber as primary gas flowcomponent and results in formation of at least one nitrogen-enriched andoxygen-reduced secondary gas flow which is not introduced into the atleast one combustion chamber.

Of particular advantage of this conduct of the process claimed for theinvention is accordingly the more or less casual possibility ofbranching nitrogen off an essentially unimpeded primary air flow asintake air flow, since the porous solid-state walls effecting oxygenenrichment are mounted along the path of flow of the intake air in sucha way that this flowing past or sweeping past of the intake air sufficesto effect oxygen enrichment and accordingly nitrogen reduction in thecombustion air flow introduced into the combustion chamber. That is tosay, in the solution claimed for the invention, the flow of thecombustion air drawn in is essentially unimpeded, while in the prior artas disclosed measures are taken which as a whole impair the flow of airto the combustion chamber or modify it, for example, by use of membranesor filters blocking the path of flow, ones through which the combustionair drawn in must flow in its entirety and which may clog with thepassage of time. In addition, no additional equipment engineeringstructures such as gas reservoirs or additional air circulation ductsare required by means of which oxygen-enriched gas produced in aseparate unit must be admixed with a flow of intake air. Consequently,conduct of the process of the invention makes certain that everythingwhich is drawn in may also flow in the direction of the combustionchamber.

Tests have shown that at a given temperature the nitrogen molecules moveat a higher speed than do the oxygen molecules, which are heavier thanthe nitrogen molecules. As a result of these different speeds, when themolecules strike the porous solid-state wall, the nitrogen molecules canpass through the porous solid-state wall with greater ease and morerapidly than can the oxygen molecules. These different transport andvelocity properties of the nitrogen molecules and oxygen molecules areaccordingly used to advantage in an especially simple way in order toeffect nitrogen reduction in the intake air in order to configure anitrogen-reduced and oxygen-enriched combustion air flow in the intakeair without the need for complex admixture of oxygen-rich gas flows orfiltering of the air flow as a whole through membranes or the likeaffecting the flow pattern. The oxygen enrichment may be coincidental.

In addition, such conduct of the process in conjunction with operationof an internal combustion engine may result in reduction of the rawemissions of nitrogen oxide, and of carbon monoxide, hydrocarbon, andsoot particles as well. Reduction of the pollutants emitted in turnresults in smaller dimensions of parts of the exhaust gas system,something which in its turn results in lower production costs.

Especially advantageous results can be obtained by compressing theintake air flow by means of at least one compressor prior to itsdelivery to the porous solid-state wall. As an alternative or inaddition, however, provision may be made such that the secondary partialgas flow is exhausted in the area of the porous solid-state wall bymeans of a vacuum device. This higher pressure level supports nitrogenmolecule reduction of the air intake flow, a pressure differenceprovided as being generated in the direction of the secondary partialgas component flow side on the primary partial gas flow side and thesecondary partial gas flow side.

In another especially preferred conduct of the process, the secondarypartial gas flow may be directed back at least in part to the intake airflow before its is introduced into the solid-state wall area, if this isfound to be necessary.

In one also especially preferred conduct of the process, a partialexhaust gas flow of an exhaust gas flow withdrawn downstream from thecombustion chamber is introduced into the nitrogen-reduced andoxygen-enriched combustion air flow is introduced into the at least onecombustion chamber. The volume of the exhaust gas flow may be reduced toadvantage by an advantageous circulation system such as this, as aresult of which, for example, the converters, such as a three-waycatalytic converter, an oxy-catalytic converter, and a particle filter,may also be made smaller, so that the dimensions of the exhaust gassystem as a whole may be made smaller. And, again, costs may be loweredas a result. In addition, it is possible by simple means to employ gasesdistinguished by an especially high heating value and in addition havingno nitrogen or nitrogen oxide components to assign a desired combustionair composition, for example, in conjunction with control action. Forexample, provision may be made such that there is introduced into thenitrogen-reduced combustion air flow in normal operation of the internalcombustion engine an amount of partial exhaust gas flow such that theoxygen component of the primary partial gas flow, that is, of thenitrogen-reduced combustion air flow, corresponds essentially to theintake air flow drawn in from the ambient atmosphere, the oxygencomponent in this instance being around 21%. As an alternative, however,provision may also be made such there is introduced into thenitrogen-reduced combustion air flow in startup operation of theinternal combustion engine, that is, during a cold start, an amount ofpartial exhaust gas flow such that the oxygen component of the primarypartial gas flow, that is, the nitrogen-reduced combustion air flow, isgreater than the oxygen component of the intake air flow drawn in fromthe ambient atmosphere. By preference the oxygen component in thisinstance may fall within the range, for example, of 21 to 40%. Theefficiency of the engine in burning of the mixture may be increased fora brief period by such oxygen enrichment without the risk thatconventional internal combustion engines might not be able to withstandthe higher combustion temperatures which might occur. In theory,however, appropriate dimensioning and design of the engines would bepossible in such a case, so that the internal combustion engine could beoperated even over a lengthy period with an increased oxygen component.

Special preference is also to be given to implementation of the processin which the amount of partial exhaust gas flow introduced into the airintake flow is controlled as a preset value by a control device as afunction of an assigned oxygen component in the combustion air flow. Itis this control device which is to compute and/or determine the actualoxygen component of the intake air flow directly and/or indirectly asthe actual value. Such control permits especially simple and rapidcompensation for any lower air density, such as in mountainous regionsor at elevated exterior temperatures.

In another preferred conduct of the process provision is also made suchthat the partial exhaust gas flow introduced into the intake air streamis established so that in the at least one combustion chamber acombustion air flow with more or less constant gas volume is availablefor formation of a mixture with a fuel. This ensures that a more or lessconstant gas volume is drawn into the combustion chamber each time forthe purpose of continuous combustion.

The advantages indicated in the foregoing in connection with the processapply to the device as well, so that they will not be discussed furtherat this point.

The invention will be described in detail below with reference to thedrawing, in which the sole FIGURE illustrates in diagram form conduct ofthe process claimed for the invention, with an intake air flow 1 whichis drawn in from the ambient atmosphere, is compressed in a compressor2, and subsequently flows, at a pressure p1, which is higher thanatmospheric pressure, past or along a porous solid-state wall 5 of areduction device 4. The porous solid-state wall 5 has a pore size of thepores 6 such that, of the nitrogen and oxygen molecules of the intakeair flowing along the porous solid-state wall 5, a higher number ofnitrogen molecules of the air intake flow than oxygen molecules flowthrough the porous solid-state wall 5 from the air intake flow. There isthereby formed along the primary flow path both a nitrogen-reduced andoxygen-enhanced combustion air flow which may be introduced into theinternal combustion engine 7 and a nitrogen-enriched and oxygen-reducedsecondary partial gas flow 9 which is not introduced into the internalcombustion engine 7. A pressure level p2 lower than the higher pressurelevel p1 assigned by the compressor 2 in the area of the intake air flowpath 3 as primary flow direction predominates in the secondary partialgas flow 9.

As is indicated by broken lines in the FIGURE, the secondary gas flow orflows 9 optionally may also be reintroduced into compressor 2 incirculation.

The nitrogen-reduced and oxygen-enriched primary partial gas flow 8leaving the reduction device 4 is then conducted as combustion air flowto a combustion chamber of the internal combustion engine 7. As is alsoillustrated in greatly simplified diagrammatic form in the FIGURE, apartial exhaust gas flow 11 withdrawn from the exhaust gas flow 10 may,in conjunction with a control device 12 shown here in diagrammatic formonly, be returned to the primary partial gas flow 8 by means of partialexhaust gas return for the purpose, for example, of constantlyintroducing in normal operation of the internal combustion engine 7 apartial exhaust gas flow amount into the nitrogen-reduced combustion airflow as primary gas flow such that the oxygen component of the primarypartial gas flow 8 corresponds approximately to that of the intake airflow 1 drawn from the ambient atmosphere, that is, in this instanceamounts essentially to 21%. The admixing may in this instance beeffected in an admixture device 13.

As an alternative, however, during start up operation, that is, forexample, during cold starting of the internal combustion engine 7, anamount of partial exhaust gas flow may be introduced into the primarypartial gas flow 8 such that the oxygen component of the primary partialgas flow 8 is greater than the oxygen component of the intake air flowdrawn from the ambient atmosphere, that is, may be greater than 21%. Theamount of partial exhaust gas flow 11 introduced into the primarypartial gas flow 8 is controlled as preset value by means of the controldevice 12, which directly or indirectly calculates and/or determines theactual oxygen component in the primary partial gas flow 8 as an actualvalue, for example, by means of a conventional oxygen probe, which isnot shown here.

1. A method of supplying a combustion gas to an internal combustion,engine, comprising: guiding a stream of ambient air containing nitrogenand oxygen molecules through an open passageway defined by auencompassing body penetrable by said nitrogen and oxygen molecules andhaving a pore size configured to permit a more ready penetrationtherethrough of said nitrogen molecules than said oxygen molecules,imposing a pressure drop across said encompassing body, therebyconverting said stream into an oxygen enriched stream; and introducingsaid oxygen enriched stream into at least one combustion chamber of saidengine.
 2. A method according to claim 1 including pressurizing saidambient air guided through said encompassing body.
 3. A method accordingto claim 1 including providing an increased pressure drop across saidencompassing body.
 4. A method according to claim 1 including applying avacuum to the nitrogen molecules emanating from said encompassing body.5. A method according to claim 1 including recirculating a portion ofsaid nitrogen molecules to said stream of ambient air guided throughsaid encompassing body.
 6. A method according to claim 5 includingrecirculating a sufficient amount of said exhaust gases to said oxygenenriched stream such that the oxygen component of said oxygen enrichedstream is greater than the oxygen component of said drawn ambient air inthe range of 21% to 40%.
 7. A method according to claim 1 includingrecirculating a portion of the exhaust gases emanating from said engineto said oxygen enriched stream.
 8. A method according to claim 7including recirculating a portion of said exhaust gases to said oxygenenriched stream in such proportions so as to simulate the constituencyof said ambient air, at selected modes of operation of said engine.
 9. Amethod according to claim 7 including recirculating a portion of saidexhaust gases to said oxygen enriched stream in such proportion so thatthe oxygen component of the stream injected into the engine is greaterthan the oxygen component of said drawn ambient air.
 10. A methodaccording to claim 9 including monitoring the oxygen component of saidoxygen enriched stream and controlling the recirculation of a portion ofsaid exhaust gases to said oxygen enriched stream to provide an oxygencontent of a preset value.
 11. A method according to claim 10 whereinsaid preset value is established to provide a selected fuel/air mixture.12. A method according to claim 1 wherein said drawn stream of ambientair is conditioned to cause the nitrogen molecules thereof to flow at avelocity greater than the velocity of the oxygen molecules thereof. 13.A method according to claim 12 wherein said drawn stream of ambient airis conditioned by compression.
 14. A device for supplying a combustiongas to an internal combustion engine, comprising: a solid body formed ofa porous material penetrable by oxygen and nitrogen molecules, having apore size configured to permit a more ready penetration therethrough ofnitrogen molecules than oxygen molecules, and an open passagewaytherethrough encompassed by said porous body, provided with an inletcommunicable with an ambient air intake an outlet communicable with acombustion cylinder of said engine, wherein upon guidance of a stream ofambient air containing oxygen and nitrogen molecules through saidpassageway encompassed by said porous body, a pressure differential isimposed between said encompassed passageway and the exterior of saidporous body, thereby converting said stream of ambient air into anoxygen enriched stream.
 15. A device according to claim 14 includingmeans for pressurizing said ambient air injected through said body. 16.A device according to claim 14 including means for providing a pressuredrop across said body between said passageway and the exterior thereof.17. A device according to claim 14 including means for recirculating aselected portion of exhaust gases of said engine to said oxygen enrichedstream.
 18. A device according to claim 17 including means forcontrolling the amount of said exhaust gas recirculated to said oxygenenriched stream.
 19. The device according to claim 14 including meansfor conditioning said ambient air drawn into said unimpeded passageway,to cause the nitrogen molecules thereof to flow at a velocity greaterthan the velocity of the oxygen molecules thereof.
 20. The deviceaccording to claim 19 wherein said means for conditioning said drawnstream of ambient air comprises a compressor.